Separate status return for "multiple credentials found"

Currently, the AI agent can't differentiate between "no login found" and "multiple logins found". Here's what my AAC console shows:

```
▸ Credential request - domain: google.com
✗ No credential found in vault for domain: google.com
[bitwarden] bw get item failed: More than one result was found. Try getting a specific object by `id` instead. The following objects were
found:
✗ Credential denied: (unknown)
```

This prevents the agent from being able to do anything further.

Start by tracing the credential request handling and the Bitwarden `bw get item` failure shown in the AAC console. Check how the “more than one result was found” error becomes “No credential found” and “Credential denied: (unknown)”. Done means the agent receives a distinct status for multiple credentials instead of treating it as no login found.

Written by the indexing model from the issue text.